Lasers have enjoyed a wide range of practical applications. It is desired to provide laser operations that provide a succession of stepped diverse laser beam intensities. A laser beam having a succession of stepped diverse beam intensities may find a wide divergence of applications. For illustrating the present invention, an application of the invention to calibrating a laser for recording data on a magneto-optical disk is shown and described. In the application to magneto-optical disks, a rapid succession of diverse laser beam intensities is desired.
In recording of any kind, including recording on optical disks, it is a continuing desire to increase the areal density of the recording. One way to increase such areal density is to increase lineal recording density along tracks on an optical disk. Earlier recording techniques employed magnetic transitions for recording and indicating binary information. Sensing these transitions produce output pulses indicating the recorded binary information. To successfully record binary information, all such magnetic transitions should be in a so-called transition position, also called a cell. Such data recording is termed pulse-position modulation (PPM). PPM can take many forms such as non-return-to-zero change on one's recording (NRZI). Non data or clock transitions were then added to NRZI recording to produce the well-known phase-encoding and frequency-modulation recording. In all of these recordings binary data are indicated by data-indicating magnetic transitions using known rules. Later, rather than representing user data values, such indications indicate 1's and 0's of a recording code, such as a d,k code. Even with all of these advances in the recording art, intersymbol interference (ISI) in PPM recording tends to limit the linear recording density of optical disks.
Pulse-width modulation (PWM) is desired to enhance lineal recording density over prior PPM recording techniques. Each data cell in PWM includes a mark and a gap. Duration or width of a mark indicates a block of information, such as one d,k code block. A leading recorded transition (herein arbitrarily indicated as a positive-going transition P) indicates an onset or leading edge of a mark that is usually also an onset of a new data cell. A mark-trailing or negative-going transition N is within a data cell and indicates end or edge of a mark and onset of a gap. Herein such leading and trailing transitions are respectively and arbitrarily shown as positive and negative going transitions P and N. To obtain high linear recording densities, higher than PPM densities, such PWM data cells are extremely short. As such, PWM introduces a need for an enhanced recording system. One such enhanced PWM recording system is shown in Belser et al U.S. Pat. No. 5,400,313. In this optical disk recording/reading system, a minimal number of circular marks on the optical disk record a desired run length of coding to be recorded. A preferred coding is a known d,k code having 1,7 parameters. This recording system provides for accurately locating mark-gap transitions on the optical disk, a necessity for high-density PWM recording. To record a mark, a plurality of short laser pulses having selected recording power levels are used. Belser et al show three laser pulse power levels that may be combined for recording the range of marks allowed by a recording code. The recording pulse power levels are selected based on recording patterns for accurately obtaining sharp recording edges or transitions. Such laser pulse recording levels shape the mark on the recording layer for enabling more faithful reproduction of recorded data. Co-pending commonly-assigned application by Hurst, Jr., Ser. No. 08/342,196, filed Nov. 18, 1994, teaches a multi-power-levels for a mark in a recording system in which a novel pre-heating operation is employed for obtaining enhanced recording.
Since optical disks are usually removable and made by several vendors, optical disk recording parameters vary between disks such that a separate calibration is needed for each optical disk. Therefore, it is desirable to calibrate the laser for writing on each disk as it is received into (mounted) an optical disk drive. Usually such mounting is commanded by an attaching host processor. It is important to ensure that the attaching host processor does not wait very long before accessing a mounted optical disk. Accordingly, write calibration should be accomplished in a minimal time. In accordance with this invention, a calibration procedure is provided that enables one calibration to effect calibrations of a plurality of recording power levels.